The present invention concerns a process and an apparatus for the remote measurement of uranium or plutonium in radioactive materials, such for example in waste glasses.
Hitherto, for the purposes of determining radioactive elements in radioactive materials, a sample is mechanically taken from those materials and then investigated for the presence of such elements. In that procedure the persons dealing with the investigation operation handle and operate with the sample of the material to be analyzed, with those tasks being implemented in chambers which shield the radioactive radiation and in which there are arranged gripping tongs assemblies and the like which can be operated by the operator from outside the chamber. Processing the samples in the chambers is a highly complicated operation and is therefore correspondingly time-consuming.
Therefore the object of the present invention is to provide a process and an apparatus for the remote measurement of uranium or plutonium in radioactive materials, whereby the sample of the material to be analyzed has to be handled as little as possible.
The object of the invention is attained by means of a process for the remote measuring of uranium or plutonium in radioactive materials characterized by the process steps: generating a light-emitting plasma of a sample of the radioactive material by irradiating the sample with a laser beam, detecting the emission spectrum of the plasma, during which the plasma is flushed with an inert gas selected from the group consisting of dust-free air and argon, and analyzing the emission spectrum obtained. The process is carried out in an apparatus comprising a laser generating a laser beam focussed onto a sample of a radioactive material to produce a light-emitting plasma, forming an image of a spectrum of the light emitted by the plasma in a spectrograph and analyzing the spectrum recorded by the spectrograph.
In accordance with the invention it is proposed that a laser be provided, the laser beam of which can be focussed onto the sample to be analyzed of the radioactive material. When the laser beam strikes the sample a tiny amount thereof is ablated, and for that reason this is called a quasi-non-destructive process. In this operation the laser produces a plasma of the sample, from which light is emitted. An image of the emission spectrum of the plasma is formed in a spectrograph and then evaluated by means of an analyzing unit. The spectral lines discovered then permit suitable information to be obtained about the presence of uranium or plutonium in the sample.
It is particularly advantageous if there is provided a delay unit which delays the beginning of the analyzing process, that is to say in particular mathematical integration of the measured emission spectra in respect of time, in regard to the laser pulse emission time. In that way it is possible to set an optimum signal/noise ratio of given spectral lines relative to each other, by varying that delay time. It is further possible to guarantee that analysis is only effected when the material removed from the sample is completely atomized.
The focussing unit for focussing the laser beam can be arranged directly at the laser so that a laser beam leaving the focussing unit of the laser can strike the sample directly through free space. It is further possible for the imaging unit which forms in the spectrograph the image of the light emitted by the laser-generated plasma to be arranged directly at the spectrograph itself. In this case also the emitted light passes directly through free space to the spectrograph. By virtue of the relatively large distances that the laser light and the light emitted by the sample plasma have to cover in free space, corresponding dispersion effects and losses in intensity of the laser beams can occur.
Preferably therefore on the one hand the laser beam is moved closer to the sample and on the other hand the light emitted by the sample is guided earlier in spatial terms so that the distances to be covered overall by the light beams in free space are reduced.
In such an embodiment of the invention there is provided a measuring head which can be fitted onto the sample. The feed of the laser beam to the measuring head and transmission of the light emitted by the sample from the measuring head to the spectrograph is effected in each case by means of light guides. The measuring head has a plurality of tubular connecting portions in which the lens systems of the focussing unit and the imaging unit respectively are arranged. In that assembly the optical axes of the lens systems are so oriented that the extensions thereof extend substantially through that region in space in which the laser-generated plasma of the sample occurs during the measurement procedure.
At least one feed conduit can be provided at the underside of the measuring head, through which feed conduit a flushing or scavenging fluid for shielding the plasma from the ambient air is fed to a chamber which is provided in the measuring head and in which the sample is disposed. The flushing or scavenging fluid may be an inert gas, preferably argon, or dust-free air.
To adjust optimum coupling of the laser beam into the light guide leading to the measuring head, there is provided an light guide coupling-in unit which is fixedly connected to the housing of the laser and which makes it possible for the light guide end that is towards the laser on the one hand to be rotated about its two transverse axes and on the other hand to be linearly displaced in the direction of said transverse axes and its longitudinal axis.